Conventionally, there is known an image forming system constituting an image forming apparatus that includes a main casing, and a replacement component that can be mounted in and detached from the main casing.
As such an image forming system described above, there is known a laser beam printer including a main casing, and a process cartridge that is detachably mounted in the main casing. A projecting portion is provided in an access member of the main casing, and a recessed portion into which the projecting portion is fitted is provided in the process cartridge. With this configuration, mounting of a process cartridge that matches with the main casing is permitted by fitting the projecting portion into the recessed portion, while mounting of a process cartridge that does not match with the main casing is restricted by prohibiting the projecting portion from fitting into the recessed portion.